1. Field of the Invention
The present invention relates to a piezoelectric ceramic composition for use in an ultrasonic wave motor, a piezoelectric transducer, etc.
2. Description of Related Art
As piezoelectric ceramic compositions used for an ultrasonic wave motor, an ultrasonic oscillator, a piezoelectric transducer, an igniter and the like, compositions comprised mainly of lead titanate zirconcite, as disclosed in Japanese Examined Patent Publication (Kokoku) No. 39-6277 and Japanese Unexamined Patent Publication (Kokai) No. 8-119733, for example, are known.
Japanese Examined Patent Publication (Kokoku) No. 39-6277 discloses a composition in which Sb.sub.2 O.sub.3 and MnO.sub.2 are externally added to a stoichiometric lead titanate zirconate represented by Pb(Zr.sub.x Ti.sub.y)O.sub.3 where x+y=1 and Sr partially substitutes for Pb.
Japanese Unexamined Patent Publication (Kokai) No. 8-119733 discloses a composition of Pb((Mn.sub.1 /.sub.3 Sb.sub.2 /.sub.3).sub.x Zr.sub.y Ti.sub.2)O.sub.3 where x+y+z=1, Sr partially substitutes for Pb, and the total mole of Sr and Pb is less than 1.
It is known that these compositions provide an excellent initial electric property when they are applied to a ultrasonic wave motor, etc.
However, the above known piezoelectric ceramic compositions have the following problems.
The piezoelectric ceramic compositions, although they have an excellent initial electric property, have a low fatigue resistance and therefore lack reliability. The reason therefor is thought to be that since a temperature of about 1200.degree. C. or higher is required to sinter the above known piezoelectric ceramic compositions for densification, the crystal grain size of the sintered body becomes relatively large and a microstructure, including fine ZrO.sub.2 particles deposited in grain boundaries, is formed. Also, stable commercial manufacture of the piezoelectric ceramic compositions is not easy due to a high sintering temperature, resulting in non-uniform quality of the products.
Thus, development of a piezoelectric ceramic composition which has an excellent electric property and excellent reliability and can be easily manufactured, has been demanded.
The present invention responds to the above demand and aims to provide a piezoelectric ceramic composition which can be manufactured at a temperature lower than the conventional temperature, has a small crystal grain size and is excellent in fatigue resistance.